A conventional type of hemodialysis machine is disclosed in European Patent No. 278,100. Such a dialysis machine is marketed under the tradename GAMBRO AK 200 ULTRA and is adapted to perform hemodialysis, hemodiafiltration or hemofiltration treatments.
The dialysis machine prepares a dialysis solution comprising sodium, bicarbonate, potassium, calcium, magnesium, chloride and acetate ions in suitable concentrations, as well as possibly glucose and other ions, all dissolved in water. The concentrations of the ions in the dialysis solution are generally mirror images of their concentrations in blood, where the optimum is the normal concentration of these ions in blood. Thus, if the concentration of an ion is increased in the blood over its normal concentration, the ion concentration in the dialysis solution is decreased in relation to the normal concentration. The pH of the solution is adjusted to about 7.1-7.4.
During hemodialysis treatment, the solution is used to achieve dialysis in a dialyser. The dialyser is divided into two chambers by means of a semi-permeable membrane. Blood which is to be treated passes over one side of the membrane while the dialysis solution prepared by the dialysis machine passes over the other side. Diffusion of ions takes place through the membrane in order to condition the blood and to at least partially replace the function of the kidneys. In addition, a quantity of liquid is removed from the blood since the patient is unable to get rid of surplus liquid in the normal manner. This removed liquid flowing through the membrane is called the ultrafiltrate flow.
During hemodiafiltration, the ultrafiltrate flow is increased above that which is necessary to restore the liquid balance of the patient. As replacement, an infusion solution is thus added to the blood in order to permit such increased ultrafiltration flow.
During hemofiltration, substantially no dialysis takes place, but instead the blood is filtered, whereby a portion of the ultrafiltration volume is added to the blood as an infusion solution. The difference between the ultrafiltration volume and the added substitution volume constitutes the volume of liquid which is removed from the patient in order to restore the liquid balance. The infusion solution may be added upstream of the dialyser or hemofilter in a process called "pre-infusion", or downstream of the dialyser or hemofilter in a process called "post-infusion".
In order to effect the infusion flow, the dialysis machine includes an infusion pump which is connected to an outlet for infusion solution on the dialysis machine. The infusion solution is normally the same as the dialysis solution. The infusion solution passes through the infusion pump, and a sterile filter, and is then fed to the patient's blood. The infusion pump may be a so-called peristaltic pump, as is used in the above-mentioned GAMBRO AK 200 ULTRA dialysis machine.
Prior to treatment, the dialysis machine is provided with a tube set, the constituent components of which must be filled with liquid so that all air is expelled. This normally takes place in a priming step during which sterile sodium chloride solution is fed into the various tubes and components of the tube set. The conduit system of the dialysis machine is also filled with dialysis solution.
During priming of the infusion circuit, a dedicated deaeration conduit from the sterile filter is used in order that the filter may be completely filled with priming liquid so that air is expelled. The nurse generally uses forceps or a tube clamp, which is placed on the normal output conduit from the sterile filter and thereby cuts off the flow therethrough. In addition, a tube clamp is opened in the deaeration conduit from the sterile filter. After deaeration of the sterile filter, the nurse removes the forceps from the output conduit or opens the tube clamp, as well as closing the tube clamp on the deaeration conduit, and the priming continues.
Due to the human factor, the nurse may forget to remove the forceps or to open the tube clamp, which may result in no infusion taking place. This may have serious consequences for the treatment if it is not corrected.
The infusion pump may be a peristaltic pump which is driven at a predetermined speed or number of revolutions so that a desired infusion flow or volume is attained. However, such peristaltic pumps are sensitive to the pressure at the inlet, and it may therefore be desirable to calibrate the pump for the particular treatment and/or to check whether the desired infusion volume has actually being attained at a particular rotational speed of the peristaltic pump.
A peristaltic pump may exhibit leakage due to the fact that occlusion of the pump segment is not complete, which may result in zero flow.
In addition, problems may arise if the user installs a tube set which is not intended for the dialysis machine in question, for example a counterfeit copy, which may not provide a suitable infusion flow.
It may also be desirable to indicate if all air in the sterile filter has been completely expelled during priming, or if there is a blockage or leakage in the sterile filter.
One object of the present invention is to provide a method and apparatus for permitting detection of the above-mentioned operational faults.
A further object of the present invention is to provide a method and apparatus of the above-mentioned type in which substantially only components which normally form a part of a dialysis machine are used.